Offset selector



Feb 23, i957 H. AUER, JR., Ema. 3,3045

OFFSET SELECTOR 5 Sheets-Sheet 1 Filed March 26, 1964 INVENTORS J.H.AUER JR., I .AROSS BY AND JPHUFFMAN y THEIR ATTORNEY Feb. 28, 1967 L H. AUER, JR.. ETAL OFFSET SELECTOR 5 Sheets-Sheen*l 2 Filed March 26, 1964 ZOCbmm z -mwo s Y Emo/@ sm ww N cN., R A we. ooo mz Q ,m A. M QzDomSo w L W u m .1W A @moi om @E P. R lhs R J. E h. m@ @moi Edi ww mm A wm H. A .q @i J. w 7/ QZDOmFDO @MGI .1. H. AUER, JR., Ema.. ,397,146

Peb. 28, i967 OFFSET SELECTOR 5 Sheets-Sheet I5 Filed March 26, 1964 5505s@ mjo QzDomSo 20mm INVENTOR J.H.AUER JR., I .A ROSS AND J.P.HUFFMAN THEx ATTORNEY Feb. 28, 1967 J. H. AUER, JR.. ETAL. 3,307,146

oFFsET'sELEcToR Filed March 26, 1964 5 Sheets-Sheet 4 Feb- 28 3967 .1. H. AUER, JR., ETAL E OFFSET SELECTOR United States Patent O 3,307,146 OFFSET SELECTOR John H. Auer, Jr., Fairport, and Lyle A. Ross and Jerry P. Huffman, Rochester, N.Y., assignors to The Geueral Signal Corporation, Rochester, N.Y., a corporation of New York Filed Mar. 26, 1964, Ser. No. 354,886 6 Claims. (Cl. 340-35) This invention relates to traffic control systems, and more particularly to a system for selecting offsets for traffic signals along a section of highway in accordance with demands of traffic.

Offset may be defined as the number of seconds or percent of the time cycle at which a green indication appears at a given traffic control signal after a certain instant used as a time reference base. In orde-r to progress traffic smoothly along an urban arterial highway, successive traffic signals encountered by arterial vehicular traffic should be green. This requires that the offset for each successive traffic signal be greater than the offset for the preceding traffic signal. For proper control of each traffic signal, a plurality of offsets should be provided for the signal. Only one particular offset may then be selected by energization of one or more leads from a central control point to each traffic signal controller.

To avoid congestion and facilitate arterial traffic flow, it is necessary to control signal offsets in accordance with demand on the highways. Sincetraffic varies with the time of day, day of the week, weather conditions, etc., the most efficient way to achieve such control is to provide offsets for the controllers which are automatically selected in accordance with traffic demands on the highway. Although it is possible to pre-program offsets in a traffic control system, such pre-programming fails to take account of unexpected conditions; instead, pre-programming restricts operation of the controllers to a rigid schedule. This prevents the fiexibility of operation which is especially desirable under adverse Weather conditions, inadvertent traffic stoppages such as those due to vehicular mishaps, etc.

Another problem encountered particularly in traffic signal control along arterial highways in larger cities is that of controlling a relatively large number of traffic signals along an artery from a single control system in response to demands of traffic. Interconnection of the signals is necessary in order to promote smooth traffic flow, since efficient control of signals along a section of highway requires that all traffic conditions within that section be taken into account -along with significant conditions within both sections adjacent that se-ction.

The invention as herein proposed permits individual control of traffic signal offsets at each traffic signal local controller along a section of artery from a single offset selector. This is -accomplished by dividing the artery into a number of arterial sections, each section encompassing a plurality of local controllers. For an artery of length sufficient to require use of a large number of local controllers, there is associated with the controllers a plurality of offset selectors. Each offset selector provides offset sign-als for the local controllers in the arterial section associated therewith based upon actual traffic conditions within the section and specified significant conditions Within adjacent sections on either side. This is accom- 3,307,146 Patented Feb. 28, 1967 ice plished by interconnecting the offset selector for each arterial section with the offset selectors for the adjacent sections on both sides, permitting specified congestion conditions in each adjacent section to be sensed. Hence, offset changes can be produced progressively along the artery, enabling traffic to ffow through the artery within a minimum of delay.

Two traffic control parameters which may be used in combination to refiect traffic conditions -along a highway to a high degree of accuracy yare lane occupancy and volume. Lane occupancy may be defined as the percentage of highway which is vehicle-occupied at any given instant of time; however, since this is a spatial concept, continuous measurement of which is rather difficult, lane occupancy is more frequently expressed las a percentage ratio of vehicle presence time to total time at any specified point. This ratio is a close approximation of spatial lane occupancy, provided traffic is moving along at a relatively constant speed. Besides being `an Iaccurate measure of traffic conditions, the parameter of traffic lane occupancy may readily be computed with a minimum of equipment and circuit complexity.

Traffic volume may be expressed as the number of vehicles passing a particular point during .any given period of time. This parameter is a fairly accurate measure of traffic congestion, provided traffic is free-fiowing; however, as congestion increases, and speed of traffic is restricted accordingly, traffic volume no longer represents an accurate measure of traffic congestion, since the krate of vehicles passing a fixed point during a given interval of time is substantially decreased, indicating low congestion when, in actuality, congestion is at a very high level.

The invention contemplates utilization of both lane occupancy and volume parameters, in order to provide highly accurate selection of offsets in accordance with actual traffic conditions, comprising first and second level monitors, each of which selectively provides a discrete output in accordance with a given level of input voltage amplitude. The rst level monitoring me-ans is responsive to the greater one of inbound lane occupancy and volume parameters within a specified section of arterial highway, and the second level monitoring means is responsive to the greater one of outbound lane occupancy and volume parameters within the specified section of highway. Outputs of the level monitors are used to selectively control a voltage divider and phase inverter circuit which provides an output voltage in accordance with both inbound and outbound lane occupancy and inbound and outbound volume conditions within the section. The output voltage produced by the voltage divider and phase inverter circuit is then coupled to a voltage modifier which discretely alters the latter output voltage in response to a sharp change in lane occupancy in either direction, occurring within either section of highway adjacent the specified section. The output voltage produced by the voltage modifier is applied to analog-to-digital conversion means, which selectively provides one or more discrete output voltages in accordance with the amplitude of lapplied voltage, thereby producing the proper offset for the specified section.

Each level monitor comprises first and second analog comparator means having a first input responsive to analog traffic congestion voltages, a group of n switching means where n represents any integer greater than one, a plurality of reference voltages, first circuit means responsive to the switching means for controlling coupling one of the reference voltages to a second input of the first analog comparator means, second circuit means responsive to the switching means for controllably coupling another of the reference voltages to a second input of the second analog comparator means, means coupling output voltage from the first analog comparator means to the input of the (n-Uth switching means when said (n1)th switching means is deenergized, and means coupling toutput vol-tage from the second analog comparator means to 'the input of the (rb-Util switching means and from the first analog comparator means to the ynth switching means -when said (n-Uth switching means is energized.

Accordingly, one object lof this invention is to provide selection means for producing offset signals for trafic 'controllers along a highway in accordance with demands of traffic.

Another object is to pr-ovide a system for selecting offsets for traffic controllers along a highway in accordance with either volume or lane occupancy conditions, whichever is greater, in both inbound and outbound directions.

Another object is t-o provide a novel level classification circuit for selectively producing discrete output voltages in accordance with the amplitude of applied voltages.

Another object is to provide a system for selecting offsets for traffic signal controllers located along a section of a vehicular route based upon demands of existing traffic within the section and changing trafiic conditions within adjacent sections.

Another object is to provide a traffic control system for a sectionalized artery wherein traffic signal controllers for each section are independently cont-rolled from separate offset selection means which are dependent upon high volyume and high lane -occupancy conditions within the section controlled therefrom and changing lane occupancy conditions within the adjacent sections.

The foregoing and other objects and advantages of the invention will become apparent from the following detailed description when read in conjunction 'with the accompanying drawings, in which:

FIG. 1 is a block diagram of an offset selector for a section of artery situated between two adjacent sections of the artery.

FIG. 2 is a chart illustrating offset coding as produced by the koffset selector.

FIGS. 3A-3D constitute a partial schematic and partial block diagram showing the system of FIG. 1 in greater detail.

FIG. 4 is a drawing showing how FIGS. 3A-3D are to be assembled.

Turning now to FIG. l, there is shown a pair of level monitors and 11. Level monitor 10 is responsive to analog data suplied by lane occupancy and volume computers responsive to traffic in the inbound direction within the section of highway controlled by the offset selector,

vwhile outbound level monitor 11 is responsive to analog data supplied by lane occupancy and volume computers monitoring traffic in the -outbound direction within the section. The lane occupancy computers may be of the type shown in I. H. Auer, Ir., et al. application Ser. No. 305,967, filed September 3, 1963, while the volume computers may assume any one of well-known configurations.

The inbound and outbound level monitors function as analog-to-digital converters, in that they `convert analog input signals into a selected one of a plurality of discrete output signals, in accordance with the amplitude of the input voltage. These discrete output signals are used to provide amplitude and phase control of the voltage produced yby an A.C. supply 12. The amplitude and phase controlled A.C. voltage is then coupled to a voltage modivfier 14. The circuitry involved in controlling the amplitude and phase of the A.C. voltage comprises an adjustable voltage divider and phase inverter circuit, designated divider-inverter circuit 13. In this fashion, the amplitude of A.C. voltage supplied to voltage modifier 14 is controlled by the setting of divider-inverter circuit 13, which in turn is responsive to outputs from level monitors 10 and 11.

Voltage modier 14 functions to further control the amplitude of A.C. voltage coupled through the system in accordance with predetermined magnitudes of changes in lane occupancy in adjacent sections. Thus, the amplitude of A.C. voltage is controllably increased by changes in excess of a predetermined value in inbound lane occupancy within the adjacent farther-out section, and by changes above a predetermined magnitude in outbound lane occupancy occurring within the adjacent closer-in section. The modified A.C. voltage is then supplied to analog-to-digital converter 15, which energizes one or more output leads in accordance wtih the amplitude and phase of the applied input voltage. Thus, outputs `are supplied which are indicative of light offsets or of an expected preferential offset in the inbound or outbound direction, heavy offset, and a preferential offset in either the inbound or outbound direction. In addition, changes in lane occupancy of a predetermined vmagnitude in the outbound direction are supplied to the offset selector for the adjacent farther-out section, while similar changes in inbound lane xoccupancy above a predetermined magnitude are supplied to the adjacent closer-in section. Changes in lane occupancy are herein designated A LANE OCC.

The chart of FIG. 2 indicates one type of coding by which offset information may be supplied from analogto-digital converter 15 to the local controllers situated along the section of highway monitored and controlled by the offset selector. The chart indicates that energization of either the light or heavy output leads indicates either light or heavy trafic, respectively; similarly, energization of either the inbound or outbound leads indicates a preferential offset in the inbound or outbound directions, respectively. Energization of both outbound and inbound leads simultaneously indicates an average offset. Simultaneous energization of the light and outbound output leads indicates an expected preferential olfset in the outbound direction, while simultaneous energization of the light and inbound output leads indicates an expected preferential offset in the inbound direction.

Turning next to FIGS. 3A-3D arranged as illustrated in FIG. 4, for a more detailed description of the system, leads 301-310 designate leads interconnecting the apparatus of the figures. Inbound level monitor 10 is shown in detail, while outbound level monitor 11 is illust-rated in block form, since it comprises circuitry which duplicates that of inbound level monitor 10. Analog voltages from the inbound lane occupancy computer are received at the anode of a diode 101, while analog voltages from the inbound volume computer for the monitored and controlled section are received at the anode of a diode 102. The cathodes of diodes 101 and 102 are directly coupled to each other and to one input of each of analog cornparators 103 and 104. These comparators algebraically sum the input voltage applied thereto, and when the polarity of the algebraic sum changes, output voltage from the analog comparator abruptly changes from a large amplitude voltage of one polarity to a large amplitude voltage of the opposite polarity.

A pair of variable resistance networks 105 and 106 are also provided. Network 106 is identical in circuitry to that of network 105, and therefore is shown in block form. Network 105 comprises a plurality of potentiometers, here seven each providing an adjustable negative output voltage. Similarly, network 106 provides seven adjustable negative output voltages.

Level monitor 10 also comprises a plurality of switching circuits SWlW?. Since each of these switching circuits is identical in circuit configuration to that of switching circuit SW1, circuits SW2-SW7 are shown in block form. Switching circuit'SWl comprises a relay 80 controlled by a pair of transistors 81 and 82. Associated with relay 80 are contacts 110, 111, 112, 113 and 114. The heel of contact 111 resistively couples a voltage from analog comparator 103 to the base of transistor 81 through a pair of series-connected resistors 83 and 84. The polarity of voltage supplied to back contact 111 may either be negative or positive, depending upon the polarity of the algebraic sum of voltage supplied to the input of the comparator. A negative reference voltage is supplied to the input of comparator 103 from resistance network 105 through back contact 110.

The base of transistor 81 is coupled to the negative terminal of the power supply through a capacitor 85 in series with base resistor 84. The collector of transistor 81 is coupled to relay S0, the other side of which is coupled to the negative power supply terminal, The emitter of transistor 81 is coupled to ground through a forward-biased diode 118, which biases the emitter of transistor 81 slightly below ground to assure that the transistor will remain non-conductive when its base voltage is zero. The cathode of the diode is also coupled to the negative supply terminal through a pair of seriesconnected resistors 86 and 87. The base of transistor 81 is -coupled to the collector of transistor 82 through a coupling resistor 88. The collector of transistor 82 is also coupled to the point common to resistors 86 and 87. The collector of transistor 81 is coupled to the positive terminal of the power supply ythrough a pair of seriesconnected resistors 89 and 90, while the base of transistor 82 receives bias from the point common to resistors 89 and 90. The emitter of transistor 82 is grounded, and a diode 91 is shunted across relay 80 in order to shortcircuit any surges p-roduced when the relay is deenergized, thereby protecting the transistors.

Operation of switching circuit SW1 occurs in the following fashion. As long as the larger one of the positive input voltages supplied by the inbound lane occupancy computer and inbound volume computer remains below the negative amplitude of voltage supplied by variable resistor network S through back contact 110 to analog comparator 103, the output voltage produced by the analog comparator remains positive in polarity. Hence, positive bias exists on the base of transistor 81, maintaining the transistor non-conductive. Relay 80 thus remains deenergized.

However, when the larger one of the positive voltages supplied by the inbound lane occupancy and volume computers exceeds the magnitude of voltage supplied to analog comparator 103 through back contact 110, the output voltage produced by the analog comparator abruptly swings negative. This drives the base of transistor 81 negative with respect to the emitter, rendering it conductive. Current is thereupon supplied to relay 80 through transistor 81, and the base of transistor 82 is driven in a positive direction. Transistor 82, which was conducting during the time in which transistor 81 was non-conductive, is thereupon driven out of conduction. The point common to resistors 86 and 87 then swings negative, driving transistor 81 further into conduction, causing relay 80 to energize. During the relay crossover time in which the source of drive for transistor 81 is removed d-ue to front and back contacts 111 being momentarily opened, suilicient drive current is supplied to the base of transistor 81 by capacitor 85 to maintain the transistor in conduction.

When front contact 111 closes, the base of transistor 81 is coupled to the output of analog comparator 104 through a series circuit comprising back contacts 130- 135 of switching circuit SW2-SW7, respectively, and re'- sistors 83 and 84. Depending upon the amplitude of negative voltage supplied to back contact 136 associated with switching circuit SW2, relay 80 will either remain enerigzed or become deenergized. This is so, since a negative voltage is supplied to analog comparator 104 from variable resistance network 106 through a series circuit comprising back contacts 136-141 of switching circuits SW2-SW7, respectively. Assuming the amplitude of voltage at back contacts 136 is suiciently small so that the algebraic sum of input voltage supplied to analog comparator 104 is positive in polarity, a negative output voltage is produced by analog compara-tor 104 which maintains transistor `81 in conduction and relay 80 ene-rgized. It should be noted, however, that if the magnitude of negative voltage at back contact 136 were greater than the magnitude of positive voltage supplied to the input of analog comparator 104 from the inbound volume and lane occupa-ncy compute-rs, the output voltage produced by comparator 104 would be positive, and transistor 81 would thereby be driven out of conduction causing relay to deenergize. Front contact 111 would then open and back contact 111 would close, thereby resupplying negative voltage to the base of transistor 81, reenergizing relay 80. In this manner, an oscillation of relay 80 would occur. However, such condition may be entirely obviated by setting the lowermost potentiometer in variable resistor networks 10S and 106 so as to produce a smaller negative voltage on back contact 136 than exists on back contact 110. This assures that relay 80 will remain energized over a predetermined range of lthe larger one of the traiic computer output voltages.

It should be noted that while relay 80 is deenergized, positive voltage is supplied through back contact 112 and a back contact 146 associated with switching circuit SW2 to the input of switching circuit SW2, thereby maintaining the circuit in a deenergized condition. However, while relay 80 is energized, voltage produced by analog comparator 103 is coupled to back contact 146 through front contact 112. In addition, front Contact of relay 80 couples a new value of negative` voltage through a back contact 147 of switching circuit SWZ to the input of analog comparator 103. The amplituder of negative voltage supplied to the input of analog comparator '103 through back contact 147 in series with front Contact 110 is preferably of greater value than that supplied through back contact 110 when relay 80 is deenengized. Thus, if the magnitude of the larger one of the input voltage to analog comparator 103 from the inbound lane occupancy and volume computers remains below the magnitude of voltage supplied to the input of analog comparator 103 from back contact 147, output voltage supplied by analog comparator 103 is positive and is coupled through front contact 112 in series with back contact 146 to the input of switching circuit SW2, maintaining the switching circuit deenergized. However, if the absolute value of the larger one of the input voltages supplied by the inbound lane occupancy and volume cornputers to analog comparator 103 exceeds the absolute amplitude of negative volta-ge supplied to the input of analog comparator 103 through back cont-act 147, the polarity of output voltage produced by comparator 103 swings negative, providing a negative input voltage for switching circuit SW2. In fashion identical to that described for switching circuit SW1, switching circuit SW2 is energized, closing front contact 136. At this ti-me, the negative voltage appearing at front contact 136 is supplied through a series circuit comprising back contacts 137-141 of switching circuits SW3-SW7, respectively, to the input of analog comparator 104. Since the ampli tude of negative voltage at front contact 136 is selected so as to be less than the amplitude of negative voltage at back contact 147, negative input voltage is supplied to switching circuit SW2 from the output of analog comparator 104 through back contacts 131-135 of switching circuits SW3-SW7, respectively, in ser-ies with front contact 146 of switching circuit SW2. In this fashion, therefore, a rising .input voltage is supplied to analog comparators 103 and 104 from the inbound lane occupancy and volume computers closes the contacts associated with switching circuits SW1, SW2 SW7, in that order.

Outbound level monitor 11, which is identical in circuitry to inbound level monitor 10, also provides outputs from seven switching circuits. Outputs from both the inbound and outbound level monitors are supplied to divider-inverter circuit 13, for control thereof. The divider-inventer receives an A C. signal from transformer 12. A series circuit comprising a pair of resistors 150 and 151 is connected in shunt across the secondary of transformer 12. Resistor 151 has -associated therewith a plurality of taps 152-159. In addition, divider-inverter 13 also comprises contacts 114 and 161-166 associated with switching circuits SW1-SW6 respectively, and contacts 172-178 associate-d with outbound level monitor 11. Tap 152 is coupled to front contacts 166 and 178. Each remaining tap is coupled to a pair of back contacts in the following manner: tap 153 to back contacts 166 and 178, tap 154 to back contacts 165 and 177, tap

'155 to back contacts 164 and 176, tap 156 to back contacts 163 and 175, tap 157 to back contacts 162 and 174, tap 158 to'back contacts 161 and 173, and tap 159 to back contacts 172 and 114. In addition, back contact 113 is coupled -to a back contact 171 associated with outbound level monitor 11, the heel of which receives positive voltage. Front contact 114 .is coupled to the hee-l of contact 161, While the heel of contact 114 is grounded. In addition, contacts 161-166 are connected in the following manner: front contact 161 to the heel of contact 162, front Contact 162 to the heel of contact 163, front contact 163 to the heel of contact 164, front contact 164 to the heel of Contact 165 and fron-t contact 165 to the heel of contact 166. In similar fashion, contacts 172- 178 are interconnected; that is, front contact 172 to the heel of contact 173, front contact 173 to the heel of contact 174, etc. Output voltage f-rom divider-inverter 13 is supplied from the heel of contact 172 to the heel of a contact 180 of a relay 181 in the circuit of voltage moditier 14. Relay 181 is energized in response to changes in inbound lane occupancy greater than a predetermined value, occurring within the adjacent farther-out section.

As front contacts 172-178 are sequentially closed by increasing outbound lane occupancy and volume voltages supplied by the outbound l'ane occupancy and volume computers, -AC. voltage is supplied from source 12 through taps 159-152 in descending order, respectively, to the heel of contact 180. Similarly, as front contacts 114, 161, 162, 163, 164, 165 and 166 are sequentially closed, ground potential is applied to taps 158, 157, 156, 155, 154, 153 and 152, respectively, in that order. Hence, in accordance with lamplitude of voltage supplied to both level monitors, output voltage is supplied to contact 180 from any of taps 152-159, while one of taps 152-159 is grounded. In this fashion, selected amplitudes of voltage are automatically chosen from resistor 155 and supplied to the heel of contact 180 With respect to ground. For straightforward operation, the segments of resistor 151 should all be of equal ohmic value; thus, voltage appearing across any pair of adjacent taps on resistor 151 is equal in amplitude to voltage appearing across any other pair of adjacent taps on the resistor. Resistor 150 is used for adjusting the total voltage acrossresistor 151 in order to control the voltage across each segment of resistor 151.

Operation of divider-inverter 13 may best be illustrated by considering a few specific examples. For instance, consider the situation in which inbound level monitor front contacts 114, 161 and 162 are closed (denoting the fth highest inbound congestion level) and outbound level monitor front contact 172 is closed (denoting the seventh highest outbound congestion level). Ground is applied to tap 156 on resistor 151 through front contacts 114, 161, 162 and back contact 163, in series. Output voltage is supplied to the heel of contact 180 from tap 158 on resistor 151 through back contact 173 and front contact 172, in series. Since the output voltage is therefore that appearing across two segments of resistor 151, the amplitude of voltage appearing across taps 156 and 158 exists at the heel of contact 180, when referred to ground. Moreover, since the output voltage is taken from the 8 voltage divider at a point below that to which ground is applied, a specific phase relationship also exists between taps 158 and 156, which is used to determine whether the inbound or out-bound traffic congestion level is highest, as is shown, infra.

Consider next the situation in which inbound level monitor front contact 114 is closed (denoting the seventh highest inbound congestion level) and outbound level monitor front contacts 172, 173, 174, and 176 are closed (denoting the third highest outbound congestion level). In this condition, output voltage is supplied to the heel of contact from tap 154 on resistor 151, while ground is applied to tap 158 on resistor 151 through front contact 114 and back contact 161. Four voltage divider segments on resistor 151 therefore separate the output voltage tap from the ground potential tap on resistor 151, so that the output voltage referred to ground comprises the voltage across the four segments. Moreover, since the output voltage is taken from the voltage divider resistor at a point higher on the resistor than that to which ground is applied, the opposite phase relationship exists from that given in the example of the preceding paragraph.

Back contact 180 is coupled to 'a back contact 183 of a relay 18S which is responsive to changes in outbound lane occupancy above a predetermined level, occurring within the adjacent closer-in section. The heel of contact 183 is resistively coupled to the base of a a transistor 186, which, along with transistors 187 'and 188 and a relay 189 comprise a selector circuit SEL1. The collectors of transistors 186 and 187 are coupled to the base of transistor 188. Negative potential is supplied to the collectors of transistors 186 and 187 through a collector load resistor 190. The emitters of transistors 186 and 187 are grounded, While the emitter of transistor 188 is biased slightly below ground potential by the forward voltage drop across a diode having its anode grounded and its cathode negatively biased through a resistor 196. Relay 189 is energized from the collector of transistor 188, and a diode 197 is shunted across relay 189 in order to protect transistor 188 against inductively-produced surges occurring when the relay is deenergized. The 1 terminal of the secondary winding of a transformer 198 is coupled to a back contact 193 of relay 189, while the 1 ltermin'al of the secondary winding of transformer 198 is resistively coupled to the base of transistor 187 and directly coupled to front contact 193. A negative bias voltage is supplied to the centertap of the secondary winding of transformer 198 through a voltage divider 199. It should be noted that Iadditional selection circuits SELZ and SEL3 are provided, having circuitry identical to that shown in selection circuit SEL1. The heel of Contact 193 supplies one input t-o each of selection circuits SELZ and SBL3, comparable to the input to transistor 187 in selection circuit SELl, while second inputs are supplied to each of selection circuits SELZ and SEL3 from a pair of selector switches 206 and 207, respectively, comparable to the input to transistor 186 in selection circuit SEL1.

A pair of front contacts 191 and 192 of relay 189 supply A.C. voltage to the i and 1 terminals respectively of the primary winding of a transformer 200, while back contacts 191 and 192 supply A C. voltage to the 1 and t terminals respectively of the primary winding of transformer 200. A resistor 201 having taps 202, 203, 204 and 205 is connected in shunt across the secondary winding of transformer 200. The secondary 1 terminal is coupled to the heel of contact 183. Taps 203, 204 and 205 on resistor 201 are separately coupled to the contacts of select-or switch 206. Similarly, taps 202, 203 and 204 on resistor 201 are :separately coupled to the contacts of selector switch 207.

Assume now that relays 181 and 185 are deenergized, and that no voltage is present on Contact 180. Under these conditions, relay 189 is energized. This is so, since transistor 186, having zero voltage applied to its base through back contact 183, is in a continuous non-conductive condition, while transistor 187 conducts on each half cycle during which voltage at the 1 terminal on the secondary Winding of transformer 198 is negative.

Because transistors 186 and 187 employ a common collector resistor 190, collector voltage on transistors 186 and 187 is negative whenever both of the transistors are non-conductive. Thus, transistor 188 is driven into conduction during each half cycle in which both transistors 186 and 187 are non-conductive. Relay 189 is thereby energized by the pulsating collector current, and remains energized during each half cycle in which current flows through collector resistor 190 due to slow dropaway characteristics introduced by diode 197 in a manner wellknown in the art.

With zero voltage on contact 180, such as with back contacts 114 and 172 of divider-inverter circuit 13 closed, the voltage at tap 205 of resistor 201 is out-of-phase with respect to the voltage on front contact 193. Thus, since the circuitry of selection circuit SEL2 is identical to the circuitry of selection circuit SEL1, output contacts 238 and 246 remain in their deenergized condition. For similar reasons, contact 241 of selection circuit SELS also remains in its deenergized condition.

Influence of changes in lane occupancy occurring within adjacent sections is supplied through circuitry comprising an inbound selector switch 230, an outboun-d selector switch 231 and a transformer 232. Relays 181 and 185 determine when the influence of the adjacent sections is to be applied, being associated with the adjacent farther-out and closer-in sections respectively. The increments of output voltage provided on the secondary of transformer 232 are equal in amplitude to the increments of voltage provided across individual segments of resistor 151 in divider-inverter circuit 13. Taps A, B and C on in-bound selector switch 230 are coupled respectively to taps D, E and F on outbound selector switch 231. Taps C and F are coupled to the 1 terminal on the secondary winding of transformer 232, taps B and E are connected to the centertap of the secondary winding of transformer 232 and taps A and D are connected to :L- secondary winding terminal on transformer 232. Back contacts 180 of relay 181 and 183 of relay 185 are each coupled to taps C and F of the inbound and outbound selector switches. Front contact 180 is coupled to a first armature G on inbound selector switch 230, while front contact 183 is coupled to a rst armature H of outbound selector switch 231.

Increments of voltage supplied by the secondary winding of transformer 232 may be added to the output voltage provided by divider-inverter circuit 13, depending upon the condition of influence relays 181 and 185. The number of increments added for inbound or outbound inuence is selected by switches 230 and 231 respectively. Zero, one or two increments of voltage may be added -to the voltage produced by divider-inverter circuit 13, depending upon the setting of the inbound and outbound selector switches.

Voltages appearing between taps 202 and 203, 203 and 204, and 204 and 205 on resistor 201 are preferably selected so as to equal the voltage increment appearing between any two adjacent taps on resistor 151 in divider-inverter circuit 13, while voltage appearing across the lowermost segment of resistor 201 is preferably selected so as to equal one and one-half times the voltage appearing between any two .adjacent taps on resistor 151. This may be accomplished through adjustment of voltage across resistor 151 by proper choice of resistor 150.

To illustrate offset selection, assume the following conditions are in existence: front contacts 114, 161, 162 and 163 in divider-inverter circuit 13 are closed by inbound level monitor 10, while front contact 172 in the dividerinverter circuit is lclosed by outbound level monitor 11. Assume further that armature G of inbound selector switch 230 is set on tap B, armature H of outbound selector switch 231 is set on tap D, selector switch 206 couples tap 204 to selection circuit SEL2, selector switch 207 couples tap 202 to selection circuit SEL3, and relay 181 is energized. Under these circumstances, tap on resistor 151 is grounded, and output voltage produced by divider-inverter circuit 13 is provided from tap 158 of resistor 151. Hence, the three voltage increments which appear between taps 155 and 158 on resistor 151 now exist on the output of the divider-inverter circuit with respect to ground. In addition, since relay 181 is energized, selector switch 230 adds one increment of voltage to the output voltage of the divider-inverter circuit before it is supplied to the secondary winding 1 terminal of transformer 200. Since the phase of Voltage on the base of transistor 186 corresponds to the phase of voltage on the base of transistor 187, and may be designated the 1 phase, transistors 186 and 187 are both non-conductive during identical halves of each cycle. Thus, relay 189 is energized, as previously described, and the phase of voltage on the secondary winding of transformer 200 then is opposite to the phase of output voltage supplied by the divider-inverter circuit. It will be noted that input voltage supplied to selector circuit SEL2 from the secondary of transformer 198 is in phase with the voltage supplied to selection circuit SEL2 from selector switch 206. This is because the amplitude of voltage supplied to contact 183 exceeds the amplitude of voltage appearing across the lowermost two segments of resistor 201; that is, four increments of voltage having the 1 phase are supplied to contact 183, and only two and one-half increments of voltage having the i phase are algebraically added to these within the lowermost two segments of resistor 201. Hence, since both input voltages to'selection circuit SEL2 are of the 1 phase, the front contacts associated therewith are closed. However, since selector switch 207 provides an input voltage to selection circuit SEL3 from tap 202 of resistor 201, four and one-half increments of voltage having the iphase are algebraically added to the four increments of volta-ge having the phase supplied to contact 183. This results in voltage on selector switch 207 acquiring the i phase, rendering the input voltages supplied to selection circuit SEL3 out-of-phase with each other. Contact 241 thus assumes its deenergized condition. The reason for this may be understood by considering operation of selection circuit SELL Thus, whenever the phase of voltage supplied to the base of transistor 186 is opposite to that supplied t-o the base of transistor 187; that is, when ground potential is applied to a tap on resistor 151 below the tap from which output voltage from resistor 151 is taken, either transistor 186 or 187 conducts at any given time, so that current flows substantially continuously through common collector resistor 190. This maintains transistor 188 non-conductive, causing relay 189 to deenergize.

Whenever relay 189 deenergizes, the voltage applied to the primary winding of transformer 200 undergoes a phase reversal, since front contacts 191 and 192 are opened and back contacts 191 and 192 are closed. Similarly, back contact 193 closes and front contact 193 opens, so that both inputs to each of selection circuits SEL2 and SEL3 undergo a phase reversal. Hence, operation of selection circuits SEL2 and SEL3 is unaffected. However, such reversal of contacts 191, 192 and 193 is necessary, since the voltage increments appearing across the segments of resistor 201 must assume a bucking polarity with respect to the polarity of voltage appearing on contact 183. Hence, if ground potential is applied to a tap on resistor 151 below the tap from which output voltage is produced, the phase of voltage supplied to the base of transistor 186 is opposite to the phase of voltage supplied to the base of transistor 187. Under such circumstances, either transistor 186 or 187 conducts at any given time, causing relay 189 to deenergize. This closes back contacts 191, 192 and 193, thereby reversing the phase of each input voltage supplied to selector circuits SEL2 and SEL3 from transformers 198 and 200.y Moreover, the

phase reversal on transformer 200 assures that the voltage on each segment of resistor 201 is of polarity to oppose the voltage produced from divider-inverter circuit 13.

A relay 233 having associated therewith contacts 234 and 236 receives energization through back contacts 171 and 113 in series, which are situated in divider-inverter circuit 13. Hence, only under light traic conditions in both directions is this relay energized. Under these circumstances, energy is supplied through front contact 236 in series with a diode 237 to an output indicative of light oiset. On the other hand, when relay 233 is deenergized, indicating that an offset condition other than light exists, back contact 236 provides energy to the heel of contact 238 associated with selection circuit SEL2. Back contact 238 provides inbound and outbound offset information through diodes 239 and 240, respectively. Front contact 238 provides energy to the heel of contact 241 associated with selection circuit SEL3. Back contact 241 provides energization of the light offset output lead through a diode 242 in series with front contact 238 and back contact 236. The inbound offset output lead in also energized through a diode 243 in series with a front contact 194 of relay 189, front contact 238 and back contact 236, while the outbound otset output lead is energized through a diode 244 in series with back contact 194, front contact 238 and back contact 236. Those skilled in the art will recognize that diodes 237, 239, 240, 242, 243 and 244 are necessary to protect against sneak circuits, which constitute undesired current paths.

Voltage modiiier circuit 14 includes a second portion of inbound selector switch 230 comprising taps I, J and K and a second portion ot outbound selector switch 231 comprising taps L, M and N. The second portion of inbound selector switch 230 is controlled by an armature P which is ganged with armature G, while the second portion of outbound selector switch 231 includes an armature Q which is ganged with armature H. Energization of armature P is supplied from a front contact 182 of relay 181, While energization of armature Q is supplied from a front contact 184 of relay 185. A plurality of front contacts 145, 142, 143 and 144 are driven from switching circuits SW4, SWS, SW6 and SW7 respectively, in inbound level monitor 10. The heels of contacts 145, 142

'and 143 are coupled to taps I, I and K, respectively, of

inbound selector switch 230, while front contacts 145, 142, 143 and 144 are coupled to gether t-o pr-ovide energization of the heavy offset output lead. Hence, when lrelay 181 is energized, if armature P of inbound selector switch 230 is coupled to a closed one of front contacts 145, 142 or 143, the heavy oiset output lead is energized. Moreover, since the heel of contact 144 is coupled to the positive voltage source, closing of front Contact 144 energizes the heavy offset output lead regardless of inbound lane occupancy conditions in the adjacent farther-out section. Circuitry similar to that comprising contacts 145, 142, 143 and 144 also exists in outbound level monitor 11, and is likewise coupled to the heavy offset output lead, as indicated by wire 301, so that energization of relay 185 may provide energization of the heavy offset output lead, depending upon whether taps L, M or N in outbound selector switch 231 are coupled to closed front contacts in outbound level monitor 11.

Changes in lane occupancy at rates in excess of predetermined amounts are supplied to apparatus controlling trac signals in either adjacent section. Thus, outputs from the inbound and outbound lane occupancy computers for the section associated with the circuitry herein 4discussed are provided to diterentiator circuits 250 and 251, respectively. Outputs from difterentiator circuits 250 and 251 are supplied to analog comparators 252 and 253, respectively. Reference potentials are supplied to second inputs in each of analog comparator circuits 252 and 253. Output voltages produced by analog comparators 252 and 253 are coupled through amplifiers 254 and 255, respectively, to an inbound lane occupancy relay 255 and an outbound lane occupancy relay 257, respectively. Relay 256 has associated therewith a front contact 258, while relay 257 has associated therewith a front contact 259.

Energization of inbound lane occupancy relay 256 occurs in the following m-anner. Assume the output voltage from the inbound lane occupancy computer for the adjacent farther-out section changes. Diierentiator circuit 250 provides an output voltage of amplitude dependent Iupon slope ot the change in inbound lane occupancy computer -output voltage amplitude. Analog comparator 252 then compares the amplitude of voltage supplied by differentiator 250 with a predetermined reference voltage, and whenever the magnitude of dilierentiator output voltage exceeds the magnitude o the reference Voltage sup- -plied to comparator 252, an abrupt change in output voltage polarity is provided by 1comparator 252, which is amplified and supplied to inbound lane occupancy relay 256, energizing the relay. The energized condition of inbound lane occupancy relay 256 signies that a change in inbound lane occupancy in excess of the predetermined rate of change is occurring. However, when the inbound lane occupancy computer output voltage begins to level off, output voltage provided by ditterentiator 250 decreases. When the magnitude of output voltage provided by ditterentiator 25) diminishes to a value below the magnitude of the reference voltage supplied to analog comparator 252, the polarity of output voltage provided by comparator 252 again abruptly changes, and inbound lane occupancy relay 256 thereupon deenergizes. Operation of the circuitry' associated with outbound lane `occupancy relay 257 occurs in a fashion identical to that described for inbound lane occupancy relay 256 in response to changes in outbound lane occupancy occurring within the adjacent closer-in section.

With relay 233 deenergized, indicating that traic congestion conditions in either or both directions are other than light, and with front contact 246 associated with selector circuit SELZ closed, indica-ting a moderate difference in congestion levels in the inbound and outbound directions, positive voltage is supplied to the heel of a contact 229 of relay 189. Energization of relay 189 indic-ates an excess in inbound congestion over outbound traitlc congestion, while deenergization of relay 189 indicates an excess of outbound trailic congestion over inbound tratiic congestion. Front contact 229 is coupled to the heel of contact 258, while back contact 229 is coupled to the heel of :contact 259. Hence, with relay 189 energized, energization of inbound lane occupancy relay 256 provides, to the adjacent closer-in section, a signal indicative of a rate of change in inbound lane occupancy greater than a predetermined value, while when relay 189 is deenergized, energization of outbound lane occupancy relay 257 provides, to the 'adjacent farther-out section, a signal indicative of a rate of change in outbound lane occupancy greater than a predetermined val-ue.

To lbriefly recapitulate operation of the circ-uit of FIGS. 3A-3D, the level monitors 10 and 11 are responsive to the greater one of the lane occupancy and volume volt- `ages produced by lane occupancy and volume computers responsive to trai-lic in the inbound and outbound directions, respectively. In accordance with the amplitude of voltage applied to the level monitors, the amplitude and phase of A.C. voltage coupled through divider-inverter circuit 13 is affected. This voltage is then modified, if so desired, within voltage modier circuit 14, so las to increase or decrease the amplitude of output voltage produced by the divider-inverter circuit, provided that a change in lane occupancy above a predetermined rate is taking place in an adjacent section. Output voltage provided by voltage modier circuit 14 is then coupled to analog-to-digital converter 15, wherein relay 189 contained in selection circuit SELl is actuated in accordance with the phase of voltage received from voltage modiier circuit 14, which is indicative of the direction in which trafiic congestion is greatest. In addition, voltage produced by voltage modifier circuit 14 is bucked by voltage within resistor 201, requiring that the amplitude of voltage supplied by voltage modifier circuit 14 to resistor 201 must exceed two predetermined levels in order to energize both of selection circuits SEL2 and SEL3. The deenergized condition of selection circuit SEL2 energizes both the inbound and outbound offset output leads, indicating existence of an average offset. Energization of selection circuit SEL3 prevents any light offset indication by opening back contact 241. A heavy offset is indicated whenever a predetermined one of the four highest output levels of level monitor or 11 is produced, along with a signal from the appropriate adjacent section indicative of a rate of change in lane occupancy above a predetermined level, as well as whenever the highest output level of level monitor 10 or 11 is produced, regardless of adjacent section trafiic conditions. Indica-tions of a change in inbound or outbound lane occupancy occurring above a predetermined rate within the monitored section are also produced, provided at least one of the two directions of traffic within the section is not at a light congestion level, and provided further that the difference between congestion levels in either direction within the section is of sufficient magnitude to energize selection circuit SEL2.

Thus, there has been shown an offset selector utilizing both lane occupancy and volume parameters in order to provide accurate selection of offsets in accordance with actual traffic conditions. The system utilizes novel level classification circuits for selectively producing discrete output voltages in accordance with Iamplitude of applied input voltages, and facilitates traffic movement by providing control for a sectionalized artery wherein traffic signal controllers for each section are independently controlled from separate offset selection means which are dependent solely upon the volume or lane occupancy conditions within the controlled section, whichever is more significant, and changing lane occupancy con-ditions within the adjacent sections. Within each section, use is made of volume parameters at low congestion levels and lane occupancy parameters -at high congestion levels to provide highly accurate representation of traffic conditions within the section.

Although but one embodiment of the present invention has been described, it is to be specifically understood that this form is selected to facilitate in disclosure of the invention rather than to limit the number of forms which it may ass-ume; various modifications and adaptations may be applied to the specific form shown to meet requirements of practice, without in any manner departing from the spirit or scope of the invention.

What is claimed is:

1. In 'a traffic control system, means for selecting offsets in accordance with actual trafiic conditions comprising, inbound lane occupancy measuring means responsive only to inbound trafiic and producing a signal representative of inbound lane occupancy, inbound volume measuring means responsive only -to inbound traffic and producing a signal represent-ative of inbound volume, fi-rst level monitoring means having said inbound lane occupancy and volume signals applied thereto and providing a selected one of a plurality of outputs in accordance with their amplitude, outbound lane occupancy measuring means responsive only to outbound trafiic and producing a signal representative of outbound lane occupancy, outbound volume measu-ring means responsive only to outbound trafiic and producing a signal representative of outbound volume, second level m-onitoring means having said outbound lane occupancy and volume signals applied thereto and providing a selected one of a plurality of outputs in accordance with their amplitude, a signal source, means controlled by the outputs of said first and second level monitoring means for controlling the signal produced by said source, and output means controlled by said signal provided by said source for selecting a particular one of said offsets.

2. The means of claim 1 wherein the means controlled by the outputs of said first and second level monitoring means comprises volt-age divider means having a plurality of taps, means coupling said signal produced by said source across said voltage divider means, means responsive to said first level monitoring means for applying ground potential to -any one of said taps, and means responsive to the second level monitoring means for coupling the signal from any one of said taps to said output means.

3. The means of claim 1 wherein each said level monitoring means comprises first and second analog comparator means, each said comparator means having a first input responsive to said inbound Ilane occupancy and volume signals, at least a pair of switching means, a plurality of reference voltages, first circuit means controlled by said switching means for controllably coupling one of the reference voltages to a second input of the first analog comparator means, second circuit means controlled by said switching means for controllably coupling another of the reference voltages to a second input of said second analog comparator means, means coupling the output voltage from said first analog comparator means tothe input of -a first one of the switching means when said rst switching means is deenergized, and means coupling the output voltage from the second analog cornparator means to the input of the first switching means and from the first analog comparator means to the input of the second switching means when said first switching means is energized.

4. The means of claim 1 wherein each said level monitoring means comprises first and second analog comparator means, each said comparator means having a first input responsive to said inbound lane occupancy and volume signals, a group of n switching means where n represents any integer greater than l, a plurality of refe-rence voltages, first circuit means controlled by said switching means for controllably coupling one of said reference voltages to a second input of said first analog comparator means, second circuit means controlled by said switching means for controllably coupling another of said reference voltages to a second input of said second analog comparator means, means coupling the output voltage from first analog comparator means to the input of the (n-1)th switching means when said (n-l)th switching means is deenergized, and means coupling the output voltage from the second analog comparator means to the input of the (n-1)th switching means and from the first analog comparator means to the input of the nth switching means when said (rz-l)th switching means is energized.

S. In a traffic control system, means for selecting offsets in accordance with actual trafiic conditions comprising, inbound lane occupancy measuring means and outbound lane occupancy measuring means each producing a signal representative of lane occupancy of a corresponding direction of trafiic, first and second level monitors receiving said lane occupancy signals produced respectively by said inbound and outbound lane occupancy measuring means and each producing a selected one of a plurality of discrete outputs in accordance with the level of lane occupancy signal applied thereto, an alternating-current means source, means coupling said inbound and outbound lane occupancy signals to said source to control the phase and amplitude of said voltage, and means controlled by the phase and amplitude of said voltage for selecting a desired one of a plurality of offsets.

6. The system of claim 5 in which both said inbound and outbound lane occupancy measuring means produce signals representative of lane occupancy of trafiic only in a predetermined section of highway, said system further including second lane occupancy measuring means responsive only to trafiic in an adjacent section lying to one 3,307,146 15. 16 side of said predetermined section and third lane occu- References Cited bythe Examiner pancy measuring means responsive only to traffic in an UNITED STATES PATENTS adjacent section lying to the other side of said predetersive to changes in the lane occupancy signals produced l. by said second and third lane occupancy measuring NEIL C' READ P'mmry Emmme' means for controlling the amplitude of the signal pro- THOMAS B. HABECKER, Examiner. duced by said alternating-current source. lo 

1. IN A TRAFFIC CONTROL SYSTEM, MEANS FOR SELECTING OFFSETS IN ACCORDANCE WITH ACTUAL TRAFFIC CONDITIONS COMPRISING, INBOUND LANE OCCUPANCY MEASURING MEANS RESPONSIVE ONLY TO INBOUND TRAFFIC AND PRODUCING A SIGNAL REPRESENTATIVE OF INBOUND LANE OCCUPANCY, INBOUND VOLUME MEASURING MEANS RESPONSIVE ONLY TO INBOUND TRAFFIC AND PRODUCING A SIGNAL REPRESENTATIVE OF INBOUND VOLUME, FIRST LEVEL MONITORING MEANS HAVING SAID INBOUND LANE OCCUPANCY AND VOLUME SIGNALS APPLIED THERETO AND PROVIDING A SELECTED ONE OF A PLURALITY OF OUTPUTS IN ACCORDANCE WITH THEIR AMPLITUDE, OUTBOUND LANE OCCUPANCY MEASURING MEANS RESPONSIVE ONLY TO OUTBOUND TRAFFIC AND PRODUCING A SIGNAL REPRESENTATIVE OF OUTBOUND LANE OCCUPANCY, OUTBOUND VOLUME MEASURING MEANS RESPONSIVE ONLY TO OUTBOUND TRAFFIC AND PRODUCING A SIGNAL REPRESENTATIVE OF OUTBOUND VOLUME, SECOND LEVEL MONITORING MEANS HAVING SAID OUTBOUND LANE OCCUPANCY AND VOLUME SIGNALS APPLIED THERETO AND PROVIDING A SELECTED ONE OF A PLURALITY OF OUTPUTS IN ACCORDANCE WITH THEIR AMPLITUDE, A SIGNAL SOURCE, MEANS CONTROLLED BY THE OUTPUTS OF SAID FIRST AND SECOND LEVEL MONITORING MEANS FOR CONTROLLING THE SIGNAL PRODUCED BY SAID SOURCE, AND OUTPUT MEANS CONTROLLED BY SAID SIGNAL PROVIDED BY SAID SOURCE FOR SELECTING A PARTICULAR ONE OF SAID OFFSETS. 